Plasma etching unit

ABSTRACT

The present invention is a plasma etching method including: an arranging step of arranging a pair of electrodes oppositely in a chamber and making one of the electrodes support a substrate to be processed in such a manner that the substrate is arranged between the electrodes, the substrate having an organic-material film and an inorganic-material film; and an etching step of applying a high-frequency electric power to at least one of the electrodes to form a high-frequency electric field between the pair of the electrodes, supplying a process gas into the chamber to form a plasma of the process gas by means of the electric field, and selectively plasma-etching the organic-material film of the substrate with respect to the inorganic-material film by means of the plasma; wherein a frequency of the high-frequency electric power applied to the at least one of the electrodes is 50 to 150 MHz in the etching step.

FIELD OF THE INVENTION

The present invention relates to a plasma etching method ofplasma-etching an organic-material film, such as alow-dielectric-constant film (low-k film), formed on a substrate to beprocessed, such as a semiconductor wafer, by using an inorganic-materialfilm as a mask.

DESCRIPTION OF THE RELATED ART

In a wiring step of a semiconductor device, an interlayer dielectricfilm, which has been formed between wiring layers, may be etched inorder to electrically connect the wiring layers. Recently, it has beenrequested to use a film having a lower dielectric constant as theinterlayer dielectric film, in order to achieve more speeding-up of thesemiconductor device. Some organic-material films have started to beused as such a film having a lower dielectric constant.

Etching process for the organic-material films is carried out by aplasma etching by using an inorganic-material film such as asilicon-oxide film as a mask. Specifically, a pair of oppositeelectrodes is arranged in a chamber in such a manner that the electrodesare vertically opposite, a semiconductor wafer (hereafter, referred toas a mere “wafer”) is placed on a lower electrode, and a high-frequencyelectric power of about 13.56 to 40 MHz is supplied to the lowerelectrode to carry out the etching process.

However, under a conventional etching condition, when anorganic-material film is etched by using an inorganic-material film as amask, in order to increase plasma density to achieve a higher etchingrate, a self-bias electric voltage has to be raised. However, if theself-bias electric voltage is raised, an etching selective ratio of theorganic-material film with respect to the inorganic-material film as amask may be decreased. That is, under the conventional etchingcondition, a high etching rate and a high etching selective ratioconflict with each other.

SUMMARY OF THE INVENTION

This invention is developed by focusing the aforementioned problems inorder to resolve them effectively. An object of the present invention isto provide a plasma etching method that can etch an organic-materialfilm with a high etching rate and a high etching selective ratio withrespect to an inorganic-material film, when the organic-material film isetched by using the inorganic-material film as a mask.

According to a result of study by the inventors, in the etching processof the organic-material film, plasma density is dominant, and ion energycontributes only a little. On the other hand, in the etching process ofthe inorganic-material film, both the plasma density and the ion energyare necessary. Thus, in order to raise an etching rate of theorganic-material film and in order to raise an etching selective ratioof the organic-material film with respect to the inorganic-materialfilm, the plasma density has to be high and the ion energy has to be lowto some extent. In the case, the ion energy of the plasma indirectlycorresponds to a self-bias electric voltage of an electrode at theetching process. Thus, in order to etch the organic-material film with ahigh etching rate and a high etching selective ratio, finally, it isnecessary to etch the organic-material film under a condition of highplasma density and low bias. According to a further result of study bythe inventors, when the frequency of the high-frequency electric powerapplied to the electrode is high, a condition wherein the plasma densityis high and the self-bias electric voltage is small can be generated.

The present invention is a plasma etching method comprising: anarranging step of arranging a pair of electrodes oppositely in a chamberand making one of the electrodes support a substrate to be processed insuch a manner that the substrate is arranged between the electrodes, thesubstrate having an organic-material film and an inorganic-materialfilm; and an etching step of applying a high-frequency electric power toat least one of the electrodes to form a high-frequency electric fieldbetween the pair of the electrodes, supplying a process gas into thechamber to form a plasma of the process gas by means of the electricfield, and selectively plasma-etching the organic-material film of thesubstrate with respect to the inorganic-material film by means of theplasma; wherein a frequency of the high-frequency electric power appliedto the at least one of the electrodes is 50 to 150 MHz in the etchingstep.

According to the present invention, since the frequency of thehigh-frequency electric power applied to the electrode is 50 to 150 MHz,which is higher than prior art, although the plasma has high density, alower self-bias electric voltage can be achieved. Thus, theorganic-material film can be etched with a high etching rate and a highetching selective ratio with respect to the inorganic-material film.

It is more preferable that the frequency of the high-frequency electricpower applied to the electrode is 70 to 100 MHz. In addition, it ispreferable that plasma density in the chamber is 5×10¹⁰ to 2×10¹¹ cm⁻³,and that a self-bias electric voltage of an electrode is not higher than900 V.

In addition, the present invention is a plasma etching methodcomprising: an arranging step of arranging a pair of electrodesoppositely in a chamber and making one of the electrodes support asubstrate to be processed in such a manner that the substrate isarranged between the electrodes, the substrate having anorganic-material film and an inorganic-material film; and an etchingstep of applying a high-frequency electric power to at least one of theelectrodes to form a high-frequency electric field between the pair ofthe electrodes, supplying a process gas into the chamber to form aplasma of the process gas by means of the electric field, andselectively plasma-etching the organic-material film of the substratewith respect to the inorganic-material film by means of the plasma;wherein, in the etching step, plasma density in the chamber is 5×10¹⁰ to2×10¹¹ cm⁻³, and a self-bias electric voltage of an electrode is nothigher than 900 V.

According to the present invention, since the plasma is generated in acondition wherein the plasma density in the chamber is 5×10¹⁰ to 2×10¹¹cm⁻³ and wherein the self-bias electric voltage of an electrode is nothigher than 900 V, the organic-material film can be etched with a highetching rate and a high etching selective ratio with respect to theinorganic-material film.

It is preferable that power density of the high-frequency electric poweris 2.12 to 4.25 W/cm².

In addition, it is preferable that a pressure in the chamber is 13.3 to106.7 Pa or 1.33 to 6.67 Pa.

In addition, it is preferable that the high-frequency electric power isapplied to an electrode supporting the substrate to be processed. In thecase, a second high-frequency electric power of 500 kHz to 27 MHz may beapplied to the electrode supporting the substrate to be processed, thesecond high-frequency electric power being overlapped with thehigh-frequency electric power. By overlapping the second high-frequencyelectric power of a lower frequency with the high-frequency electricpower, plasma density and ion drawing effect can be adjusted so that anetching rate of the organic-material film can be raised more while ahigh etching selective ratio with respect to the inorganic-material filmcan be assured. It is preferable that a frequency of the secondhigh-frequency electric power is 13.56 MHz or 3.2 MHz. If the frequencyof the second high-frequency electric power is 3.2 MHz, it is preferablethat power density of the second high-frequency electric power is nothigher than 4.25 W/cm².

In addition, the present invention is a plasma etching methodcomprising: an arranging step of arranging a pair of electrodesoppositely in a chamber and making one of the electrodes support asubstrate to be processed in such a manner that the substrate isarranged between the electrodes, the substrate having anorganic-material film and an inorganic-material film; and an etchingstep of applying a high-frequency electric power to at least one of theelectrodes to form a high-frequency electric field between the pair ofthe electrodes, supplying a process gas into the chamber to form aplasma of the process gas by means of the electric field, andselectively plasma-etching the organic-material film of the substratewith respect to the inorganic-material film by means of the plasma;wherein, in the etching step: a pressure in the chamber is 13.3 to 106.7Pa; the first high-frequency electric power is applied to an electrodesupporting the substrate to be processed; a frequency of the firsthigh-frequency electric power is 50 to 150 MHz; power density of thefirst high-frequency electric power is 2.12 to 4.25 W/cm²; a secondhigh-frequency electric power is applied to the electrode, the secondhigh-frequency electric power being overlapped with the firsthigh-frequency electric power; a frequency of the second high-frequencyelectric power is 500 kHz to 27 MHz; power density of the secondhigh-frequency electric power is not higher than 4.25 W/cm²; plasmadensity in the chamber is 5×10¹⁰ to 2×10¹¹ cm⁻³; and a self-biaselectric voltage of an electrode is not higher than 900 V.

According to the above condition, vertical component of ion energy ontothe substrate to be processed can be relatively reduced, so that theorganic-material film can be etched with a high etching selective ratiowith respect to the inorganic-material film and with a high etchingrate. In particular, when a hole is etched, a very high etching rate canbe achieved while a high etching selective ratio can be maintained.

In addition, the present invention is a plasma etching methodcomprising: an arranging step of arranging a pair of electrodesoppositely in a chamber and making one of the electrodes support asubstrate to be processed in such a manner that the substrate isarranged between the electrodes, the substrate having anorganic-material film and an inorganic-material film; and an etchingstep of applying a high-frequency electric power to at least one of theelectrodes to form a high-frequency electric field between the pair ofthe electrodes, supplying a process gas into the chamber to form aplasma of the process gas by means of the electric field, andselectively plasma-etching the organic-material film of the substratewith respect to the inorganic-material film by means of the plasma;wherein, in the etching step: a pressure in the chamber is 1.33 to 6.67Pa; the first high-frequency electric power is applied to an electrodesupporting the substrate to be processed; a frequency of the firsthigh-frequency electric power is 50 to 150 MHz; power density of thefirst high-frequency electric power is 2.12 to 4.25 W/cm²; a secondhigh-frequency electric power is applied to the electrode, the secondhigh-frequency electric power being overlapped with the firsthigh-frequency electric power; a frequency of the second high-frequencyelectric power is 500 kHz to 27 MHz; power density of the secondhigh-frequency electric power is not higher than 0.566 W/cm²; plasmadensity in the chamber is 5×10¹⁰ to 2×10¹¹ cm⁻³; and a self-biaselectric voltage of an electrode is not higher than 400 V.

According to the above condition, ion energy itself can be controllednot higher than energy by which the inorganic-material film can bespattered, so that an etching selective ratio of the organic-materialfilm with respect to the inorganic-material film can be remarkablyraised while a high etching rate is maintained. In addition, surfaceresidue is substantially not left. In addition, when theinorganic-material film is used as a mask, a CD-shift of the mask can beremarkably small.

In the above features, as the organic-material film, a materialincluding O, C and H, or another material including Si, O, C and H maybe used. As the inorganic-material film, a material comprising at leastone of a silicon oxide, a silicon nitride and a silicon oxinitride maybe used.

In addition, the present invention is a plasma etching unit comprising:a chamber configured to contain a substrate to be processed having anorganic-material film and an inorganic-material film; a pair ofelectrodes arranged in the chamber, one of the pair of electrodes beingconfigured to support the substrate to be processed; a process-gassupplying system configured to supply a process gas into the chamber; agas-discharging system configured to discharge a gas in the chamber; anda high-frequency electric power source configured to supply ahigh-frequency electric power for forming a plasma to at least one ofthe electrodes; wherein a frequency of high-frequency electric powergenerated by the high-frequency electric power source is 50 to 150 MHz.

Preferably, the high-frequency electric power source is adapted to applythe high-frequency electric power to an electrode supporting thesubstrate to be processed. In the case, it is preferable that the plasmaetching unit further comprises a second high-frequency electric powersource configured to apply a second high-frequency electric power of 500kHz to 27 MHz to the electrode supporting the substrate to be processed,the second high-frequency electric power being overlapped with thehigh-frequency electric power. It is preferable that the secondhigh-frequency electric power is of 13.56 MHz or 3.2 MHz.

Herein, because of the Paschen's law, an electric-discharge startingvoltage Vs takes a local minimum value (Paschen's minimum value) when aproduct pd of a gas pressure p and a distance d between the electrodestakes a certain value. The certain value of the product pd thatcorresponds to the Paschen's minimum value is smaller when the frequencyof the high-frequency electric power is higher. Thus, when the frequencyof the high-frequency electric power is high, in order to decrease theelectric-discharge starting voltage Vs to facilitate and stabilize theelectric-discharge effect, the distance d between the electrodes has tobe reduced, if the gas pressure p is constant. Thus, in the presentinvention, it is preferable that the distance between the electrodes isshorter than 50 mm. In addition, when the distance between theelectrodes is shorter than 50 mm, residence time of the gas in thechamber can be shortened. Thus, reaction products can be efficientlydischarged, and etching stop can be reduced.

In addition, it is preferable that the plasma etching unit furthercomprises a magnetic-field forming unit configured to form a magneticfield around a plasma region between the pair of electrodes.

When the frequency of the applied high-frequency electric power is high,the etching rate may be higher in a central portion as a feedingposition compared with in a peripheral portion. However, if a magneticfield is formed around a plasma region between the pair of electrodes,plasma confining effect can be achieved so that the etching rate on thesubstrate to be processed arranged in a processing space can be madesubstantially the same between in an edge portion (peripheral portion)of the substrate to be processed and in a central portion thereof. Thatis, the etching rate can be made uniform.

It is preferable that strength of the magnetic field formed around aplasma region between the pair of electrodes by the magnetic-fieldforming unit is 0.03 to 0.045 T (300 to 450 Gauss).

In addition, it is preferable that a focus ring is provided around theelectrode supporting the substrate to be processed, and that when themagnetic-field forming unit forms a magnetic field around a plasmaregion between the pair of electrodes, strength of the magnetic field onthe focus ring is not lower than 0.001 T (10 Gauss) and strength of themagnetic field on the substrate to be processed is not higher than 0.001T.

When the strength of the magnetic field on the focus ring is not lowerthan 0.001 T, drift movement of electrons may be generated on the focusring, so that the plasma density around the focus ring is raised to makethe plasma density uniform. On the other hand, when the strength of themagnetic field on the substrate to be processed is not higher than 0.001T, which substantially has no effect on the substrate to be processed,charge-up damage can be prevented.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic vertical sectional view showing a plasma etchingunit of an embodiment according to the present invention;

FIG. 2 is a horizontal sectional view schematically showing a magneticannular unit arranged around a chamber of the plasma etching unit ofFIG. 1;

FIGS. 3A to 3C are explanatory views of a change of a magnetic fieldwhen segment magnets of the plasma etching unit of FIG. 1 are revolved;

FIG. 4 is a graph showing strengths of magnetic fields when the segmentmagnets of the plasma etching unit of FIG. 1 are revolved;

FIG. 5 is a view showing another example of revolving operation ofsegment magnets of the plasma etching unit of FIG. 1;

FIG. 6 is a view showing further another example of revolving operationof segment magnets of the plasma etching unit of FIG. 1;

FIG. 7 is a view showing another example of segment magnets for theplasma etching unit of FIG. 1;

FIGS. 8A to 8E are schematic views showing various arrangement examplesof the segment magnets of the plasma etching unit of FIG. 1;

FIGS. 9A and 9B are sectional views showing a structural example ofwafer to which a plasma etching process according to the presentinvention is applied;

FIG. 10 is a schematic sectional view partly showing a plasma processingunit comprising a high-frequency electric power source for generatingplasma and a high-frequency electric power source for drawing ions;

FIG. 11 is a graph showing relationships between a self-bias electricvoltage Vdc and plasma density Ne, in respective cases wherein thefrequency of the high-frequency electric power is 40 MHz or 100 MHz,when the plasma consists of argon gas;

FIG. 12 is a graph comparatively showing relationships between aself-bias electric voltage and plasma density, in respective caseswherein the plasma is formed by an Ar gas or an etching gas, when thefrequency of the high-frequency electric power is 100 MHz;

FIG. 13A is a graph showing etching rates of an organic-material film ata wafer position, in samples of respective cases wherein thehigh-frequency electric power is 500 W, 1000 W or 1500 W, when thefrequency of the high-frequency electric power is 100 MHz;

FIG. 13B is a graph showing etching rates of an organic-material film ata wafer position, in samples of respective cases wherein thehigh-frequency electric power is 500 W, 1000 W or 1500 W, when thefrequency of the high-frequency electric power is 40 MHz;

FIG. 14 is a graph showing relationships between a high-frequencyelectric power and an etching rate of the organic-material film, insamples of respective cases wherein the frequency of the high-frequencyelectric power is 40 MHz or 100 MHz;

FIG. 15 is a graph showing relationships between a high-frequencyelectric power and an etching rate of the inorganic-material film, insamples of respective cases wherein the frequency of the high-frequencyelectric power is 40 MHz or 100 MHz;

FIG. 16 is a graph showing relationships between an etching rate of theorganic-material film and a ratio (an etching rate of theorganic-material film/an etching rate of the inorganic-material film)corresponding to an etching selective ratio, in samples of respectivecases wherein the frequency of the high-frequency electric power is 40MHz or 100 MHz;

FIG. 17 is a graph showing relationships between a high-frequencyelectric power and an etching rate of the organic-material film andrelationships between a high-frequency electric power and an etchedvolume of a shoulder part of the inorganic-material film (shoulderloss), wherein the real pattern shown in FIG. 9 is used;

FIG. 18 is a graph showing relationships between an etching rate of theorganic-material film and an etching selective ratio with respect to anetching rate of the shoulder part of the inorganic-material film, inrespective cases wherein the frequency of the high-frequency electricpower is 40 MHz or 100 MHz, wherein the real pattern shown in FIG. 9 isused;

FIG. 19 is a view for explaining a shoulder loss;

FIG. 20 is a graph comparatively showing relationships between an Ar-gasflow rate and a pressure difference ΔP of a central portion of the waferand a peripheral portion thereof, in respective cases wherein anelectrode gap is 25 mm or 40 mm, wherein the Ar gas is used as a plasmagas;

FIG. 21 is a graph showing relationships between the electric power of3.2 MHz and an etching rate of the organic-material film andrelationships between the electric power of 3.2 MHz and an etchingselective ratio with respect to the shoulder part, in respectivepressure conditions;

FIG. 22 is a graph showing relationships between the electric power of3.2 MHz and a top CD shift, in respective pressure conditions;

FIG. 23 is a graph showing relationships between the electric power of3.2 MHz and a bowing value, in respective pressure conditions;

FIG. 24 is a view for explaining a top CD shift;

FIG. 25 is a view for explaining a bowing value;

FIG. 26 is a graph showing etching residues, shoulder losses of theinorganic-material film (mask) and top CD shifts, in respective pressureconditions, when the bias power is zero; and

FIG. 27 is a graph showing shoulder losses of the inorganic-materialfilm (mask), top CD shifts and etching rates of the organic-materialfilm, in respective bias-power conditions, when the pressure is 3.99 Pa.

DESCRIPTION OF THE PREFERRED EMBODIMENT

An embodiment of the invention will now be described with reference tothe attached drawings.

FIG. 1 is a schematic sectional view showing a plasma etching unit usedfor carrying out the present invention. The etching unit of theembodiment includes a two-stage cylindrical chamber vessel 1, which hasan upper portion 1 a having a small diameter and an lower portion 1 bhaving a large diameter. The chamber vessel 1 may be hermetically madeof any material, for example aluminum.

A supporting table 2 is arranged in the chamber vessel 1 forhorizontally supporting a wafer W as a substrate to be processed. Thesupporting table 2 may be made of any material, for example aluminum.The supporting table 2 is placed on a conductive supporting stage 4 viaan insulation plate 3. A focus ring 5 is arranged on a peripheral areaof the supporting table 2. The focus ring 5 may be made of anyconductive material or any insulating material. When the diameter of thewafer W is 200 mmφ, it is preferable that the focus ring 5 is 240 to 280mmφ. The supporting table 2, the insulation plate 3, the supportingstage 4 and the focus ring 5 can be elevated by a ball-screw mechanismincluding a ball-screw 7. A driving portion for the elevation isarranged below the supporting stage 4 and is covered by a bellows 8. Thebellows 8 may be made of any material, for example stainless steel(SUS). The chamber vessel 1 is earthed. A coolant passage (not shown) isformed in the supporting table 2 in order to cool the supporting table2. A bellows cover 9 is provided around the bellows 8.

A feeding cable 12 for supplying a high-frequency electric power isconnected to a substantially central portion of the supporting table 2.The feeding cable 12 is connected to a high-frequency electric powersource 10 via a matching box 11. A high-frequency electric power of apredetermined frequency is adapted to be supplied from thehigh-frequency electric power source 10 to the supporting table 2. Ashowerhead 16 is provided above the supporting table 2 and oppositely inparallel with the supporting table 2. The showerhead 16 is also earthed.Thus, the supporting table 2 functions as a lower electrode, and theshowerhead 16 functions as an upper electrode. That is, the supportingtable 2 and the showerhead 16 form a pair of plate electrodes.

Herein, it is preferable that the distance between the electrodes is setto be shorter than 50 mm. The reason is as follows.

Because of the Paschen's law, an electric-discharge starting voltage Vstakes a local minimum value (Paschen's minimum value) when a product pdof a gas pressure L and a distance d between the electrodes takes acertain value. The certain value of the product pd that corresponds tothe Paschen's minimum value is smaller when the frequency of thehigh-frequency electric power is higher. Thus, when the frequency of thehigh-frequency electric power is high like the present embodiment, inorder to decrease the electric-discharge starting voltage Vs tofacilitate and stabilize the electric-discharge effect, the distance dbetween the electrodes has to be reduced, if the gas pressure L isconstant. Thus, it is preferable that the distance between theelectrodes is shorter than 50 mm. In addition, when the distance betweenthe electrodes is shorter than 50 mm, residence time of the gas in thechamber can be shortened. Thus, reaction products can be efficientlydischarged, and etching stop can be reduced.

However, if the distance between the electrodes is too short, pressuredistribution on the surface of the wafer W as a substrate to beprocessed (pressure difference between in a central portion and in aperipheral portion) may become large. In the case, problems such asdeterioration of etching uniformity may be generated. Independently ongas flow rate, in order to make the pressure difference smaller than0.27 Pa (2 mTorr), it is preferable that the distance between theelectrodes is not shorter than 35 mm.

An electrostatic chuck 6 is provided on an upper surface of thesupporting table 2 in order to electrostaticly stick to the wafer W. Theelectrostatic chuck 6 consists of an insulation plate 6 b and anelectrode 6 a inserted in the insulation plate 6 b. The electrode 6 a isconnected to a direct-current power source 13. Thus, when the powersource 13 supplies an electric power to the electrode 6 a, thesemiconductor wafer W may be stuck to the electrostatic chuck 6 bycoulomb force, for example.

The coolant passage not shown is formed in the supporting table 2. Thewafer W can be controlled at a predetermined temperature by circulatinga suitable coolant in the coolant passage. In order to efficientlytransmit heat of cooling from the suitable coolant to the wafer W, agas-introducing mechanism (not shown) for supplying a He gas onto areverse surface of the wafer W is provided. In addition, a baffle plate14 is provided at an outside area of the focus ring 5. The baffle plate14 is electrically connected to the chamber vessel 1 via the supportingstage 4 and the bellows 8.

The showerhead 16 facing the supporting table 2 is provided in a ceilingof the chamber vessel 1. The showerhead 16 has a large number of gasjetting holes 18 at a lower surface thereof and a gas introducingportion 16 a at an upper portion thereof. Then, an inside space 17 isformed between the gas introducing portion 16 a and the large number ofgas jetting holes 18. The gas introducing portion 16 a is connected to agas supplying pipe 15 a. The gas supplying pipe 15 a is connected to aprocess-gas supplying system 15, which can supply a process gas foretching. As the process gas for etching, at least one of an N₂ gas, anH₂ gas, an O₂ gas, a CO gas, an NH₃ gas, a C_(x)H_(y) gas (x and y arenatural numbers) and a rare gas such as Ar or He may be used. Forexample, a mixed gas of an N₂ gas and an O₂ gas, or a mixed gas of an N₂gas and an H₂ gas may be used.

The process gas is supplied from the process-gas supplying system 15into the space 17 of the showerhead 16 through the gas supplying pipe 15a and the gas introducing portion 16 a. Then, the process gas is jettedfrom the gas jetting holes 18 in order to etch a film formed on thewafer W.

A discharging port 19 is formed at a part of a side wall of the lowerportion 1 b of the chamber 1. The discharging port 19 is connected to agas-discharging system 20 including a vacuum pump. A pressure of aninside of the chamber vessel 1 may be reduced to a predetermined vacuumlevel by operating the vacuum pump. A transferring port for the wafer Wand a gate valve 24 for opening and closing the transferring port arearranged at another upper part of the side wall of the lower portion 1 bof the chamber vessel 1.

A magnetic annular unit 21 is concentrically arranged around the upperportion 1 a of the chamber vessel 1. Thus, a magnetic field may beformed around a processing space between the supporting table 2 and theshowerhead 16. The magnetic annular unit 21 may be caused to revolvearound a center axis thereof (along an annular peripheral edge thereof)by a revolving mechanism 25.

The magnetic annular unit 21 has a plurality of segment magnets 22 whichare supported by a holder not shown and which are arranged annularly.Each of the plurality of segment magnets 22 consists of a permanentmagnet. In the embodiment, 16 segment magnets 22 are arranged annularly(concentrically) in a multi-pole state. That is, in the magnetic annularunit 21, adjacent two segment magnets 22 are arranged in such a mannerthat their magnetic-pole directions are opposite. Thus, a magnetic lineof force is formed between the adjacent two segment magnets 22 as shownin FIG. 2, so that a magnetic field of 0.02 to 0.2 T (200 to 2000Gauss), preferably 0.03 to 0.045 T (300 to 450 Gauss), is generated onlyaround the processing space. On the other hand, in a region wherein thewafer is placed, a substantially non-magnetic field state is generated.The above strength of the magnetic field is determined because of thefollowing reasons: if the magnetic field is too strong, a fringing fieldmay be caused; and if the magnetic field is too weak, plasma confiningeffect can not be achieved. Of course, the suitable strength of themagnetic field also depends on the unit structure or the like. That is,the range of the suitable strength of the magnetic field may bedifferent for respective units.

When the above magnetic field is formed around the processing space,strength of the magnetic field on the focus ring 5 is desirably notlower than 0.001 T (10 Gauss). In the case, drift movement of electrons(E×B drift) is generated on the focus ring, so that the plasma densityaround the wafer is increased, and hence the plasma density is madeuniform. On the other hand, in view of preventing charge-up damage ofthe wafer W, strength of the magnetic field in a portion where the waferW is positioned is desirably not higher than 0.001 T (10 Gauss).

Herein, the substantially non-magnetic state in a region occupied by thewafer means a state that there is not a magnetic field affecting theetching process in the area occupied by the wafer. That is, thesubstantially non-magnetic state includes a state that there is amagnetic field not substantially affecting the wafer process.

In the state shown in FIG. 2, a magnetic field whose density is not morethan 420 μT (4.2 Gauss) is applied to a peripheral area of the wafer.Thus, plasma confining function can be achieved.

When a magnetic field is formed by the magnetic annular unit of themulti-pole state, wall portions of the chamber 1 corresponding to themagnetic poles (for example, portions shown by P in FIG. 2) may belocally whittled. Thus, the magnetic annular unit 21 may be caused torevolve along the peripheral direction of the chamber by the aboverevolving mechanism 25. Thus, it is avoided that the magnetic poles arelocally abutted (located) against the chamber wall, so that it isprevented that the chamber wall is locally whittled.

Each segment magnet 22 is configured to freely revolve around aperpendicular axis thereof by a segment-magnet revolving mechanism notshown. That is, from a state shown in FIGS. 2 and 3A wherein themagnetic poles of the segment magnets 22 are oriented toward the chamber1, adjacent two segment magnets 22 revolve synchronously and oppositelythrough a state shown in FIG. 3B to a state shown in FIG. 3C (everyother segment magnet 22 revolves in the same direction). Herein, FIG. 3Bshows a state wherein the segment magnets 22 have revolved by 45degrees, and FIG. 3C shows a state wherein the segment magnets 22 haverevolved by 90 degrees.

FIG. 4 is a graph showing relationships between a distance from thecenter of the wafer W and strength of the magnetic field, in a caseshown in FIG. 3A (curve A), in a case shown in FIG. 3B (curve B) and ina case shown in FIG. 3C (curve C). The transverse axis represents thedistance from the center of the wafer W placed on the supporting table 2in the chamber 1, and the ordinate axis represents the strength of themagnetic field. In the state shown in FIG. 3A, as shown by the curve A,a multi-pole magnetic field is formed substantially to a peripheralportion of the wafer W. On the other hand, in the state shown in FIG.3C, as shown by the curve C, there is formed substantially no magneticfield in the chamber 1. The state shown in FIG. 3B is a magnetic-fieldstate between them.

That is, when the segment magnets 22 are caused to revolve as shown inFIGS. 3A to 3C, the state wherein the multi-pole magnetic field issubstantially formed and the state wherein the multi-pole magnetic fieldis not formed can be switched. Depending on a kind of film to be etched,the multi-pole magnetic field may be effective or not. Thus, when thestate wherein the multi-pole magnetic field is formed and the statewherein the multi-pole magnetic field is not formed can be switched, asuitable etching condition can be selected correspondingly to the film.

The revolving manner of the segment magnets 22, for switching betweenthe state wherein the multi-pole magnetic field is formed and the statewherein the multi-pole magnetic field is not formed, is not limited tothe manner shown in FIG. 3. For example, as shown in FIG. 5, all thesegment magnets 22 may be configured to revolve in the same direction.Alternatively, as shown in FIG. 6, only every other segment magnet 22may be configured to revolve while the other segment magnets 22 may befixed. When the manner shown in FIG. 6 is adopted, the number ofrevolving segment magnets 22 is reduced, so that the revolving mechanismmay be made simpler. In addition, as shown in FIG. 7, one magnetic polemay consist of a set of a plurality of segment magnets, for example aset of three segment magnets 22 a, 22 b and 22 c. In the case, thesesegment magnets 22 a, 22 b and 22 c may synchronously revolve in thesame direction. Like this, if a larger number of segment magnets areused, the strength of the magnetic field can be enhanced more.

Next, arrangement examples of the segment magnets and magnetic fieldsgenerated thereby are explained.

FIGS. 8A to 8E are schematic views showing various arrangement examplesof the segment magnets.

FIG. 8A is a standard arrangement example. In the case, the segmentmagnets 22 are arranged away from a lateral wall of the chamber 1 by apredetermined distance m. A profile of magnetic field generated by thisarrangement may be adjusted by changing magnetic forces and/or verticallengths of the segment magnets 22.

In examples shown in FIGS. 8B and 8C, each segment magnet 22 isvertically bisected into a magnet 22 d and a magnet 22 e. Then, a set ofannularly arranged magnets 22 d and a set of annularly arranged magnets22 e are respectively vertically movable. As shown in FIG. 8B, when agap between the magnets 22 d and 22 e is small and a distance betweenthe magnets and a wafer edge is short, a relatively large magnetic fieldis formed in a periphery of the edge of the wafer W. On the other hand,as shown in FIG. 8C, when a gap between the magnets 22 d and 22 e islarge and a distance between the magnets and a wafer edge is long, arelatively small magnetic field is formed in a periphery of the edge ofthe wafer W. Herein, the divided magnets 22 d and 22 e may have the samemagnetization direction. However, it is more preferable that they haveopposite magnetization directions, because the same magnetic-poleportions (P portions shown in FIG. 2) are dispersed so that whittling ofthe inner-wall portion of the chamber 1 is prevented.

In examples shown in FIGS. 8D and 8E, a set of the divided magnets 22 dand a set of the divided magnets 22 e are respectively forward andbackward movable. As shown in FIG. 8D, when the magnets 22 d and 22 eare located nearer to the lateral wall of the chamber 1 than thepredetermined distance m (when the diameters of the annular magneticunits respectively formed by the magnets 22 d and 22 e are small), astronger magnetic field is formed around the processing space. On theother hand, as shown in FIG. 8E, when the magnets 22 d and 22 e arelocated further than the predetermined distance m (when the diameters ofthe annular magnetic units are large), a weaker magnetic field is formedaround the processing space.

As described above, by variously changing the arrangement of the segmentmagnets, various profiles of magnetic field can be formed. Thus, it ispreferable to arrange the segment magnets so as to obtain a requiredprofile of magnetic field.

The number of the segment magnets is not limited to the above examples.The section of each segment magnet is not limited to the rectangle, butmay have any shape such as a circle, a square, a trapezoid or the like.A magnetic material forming the segment magnets 22 is also not limited,but may be any known magnetic material such as a rare-earth magneticmaterial, ferrite magnetic material, an Arnico magnetic material, or thelike.

Next, an operation for etching a low-dielectric-constant film (low-kfilm) as an organic-material film by using the above plasma etching unitand by using an inorganic-material film as a mask is explained.

In a wafer W before being etched, as shown in FIG. 9A, anorganic-material film 42 that is a low-k film is formed as an interlayerdielectric film on a silicon substrate 41. Then, an inorganic-materialfilm 43 having a predetermined pattern is formed as a hard mask on theorganic-material film 42. Thereon, a BARC layer 44 is formed. Then, aresist film 45 having a predetermined pattern is formed thereon.

The inorganic-material film 43 consists of a material generally used asa hard mask. As a suitable example, it may be a silicon oxide, a siliconnitride, a silicon oxinitride, or the like. That is, it is preferablethat the inorganic-material film 43 consists of at least one of theabove materials.

The organic-material film 42 to be etched is a low-k film used as aninterlayer dielectric film, as described above. Thus, the dielectricconstant of the organic-material film 42 is much smaller than that of asilicon oxide which is a conventional material for an interlayerdielectric film. The low-k film of the organic-material consists of, forexample, a polyorganosiloxane-bridge bisbenzocyclobutene resin (BCB), apolyaryleneether resin (PAE) such as SiLK (commercial name) and FLARE(commercial name) made by DowChemical Company, an organic polysiloxaneresin such as methylsilsesquioxane (MSQ), or the like. Herein, theorganic polysiloxane means a material having a structure wherein afunctional group including C, H is included in a bonding-structure of asilicon oxide film, as shown below. In the structure shown below, Rmeans an alkyl group such as a methyl group, an ethyl group, a propylgroup or the like; or a derivative thereof; or an aryl group such as aphenyl group: or a derivative thereof.

In the wafer W of the above structure, the BARC layer 44 and theinorganic-material film 43 are etched while the resist film 45 is usedas a mask. The state is shown in FIG. 9B. In the step, the thickness ofthe resist film 45 is reduced by the etching.

Then, the organic-material film 42 is etched while the resist film 45and the inorganic-material film 43 are used as a mask. At first, thegate valve 24 of the unit of FIG. 1 is opened, a wafer W of thestructure shown in FIG. 9B is conveyed into the chamber 1 by means of aconveying arm, and placed on the supporting table 2. After that, theconveying arm is evacuated, the gate valve 24 is closed, and thesupporting table 2 is moved up to a position shown in FIG. 1. The vacuumpump of the gas-discharging system 20 creates a predetermined vacuum inthe chamber 1 through the discharging port 19.

Then, a predetermined process gas, for example an N₂ gas and an O₂ gas,is introduced into the chamber 1 through the process-gas supplyingsystem 15, for example at a flow rate of 0.1 to 1 L/min (100 to 1000scam). Thus, a pressure in the chamber 1 is maintained at apredetermined pressure, for example about 1.33 to 133.3 Pa (10 to 1000mTorr). Within the pressure range, in order to maintain a high etchingselective ratio with respect to the inorganic-material film and to etchthe organic-material film with a high etching rate, a relatively highpressure of 13.3 to 106.7 Pa (100 to 800 mTorr) is preferable. On theother hand, in order to achieve an etching process wherein an etchingselective ratio with respect to the inorganic-material film is veryhigh, residue is less, and accuracy of form is good, a relatively lowpressure of 1.33 to 6.67 Pa (10 to 50 mTorr) is preferable. While thepressure in the chamber 1 is maintained within such a predeterminedpressure range, a high-frequency electric power whose frequency is 50 to150 MHz, preferably 70 to 100 MHz, is supplied from the high-frequencyelectric power source 10 to the supporting table 2. In this case, powerper unit area (hereinafter, referred to as power density) is preferablywithin a range of about 1.0 to about 5.0 W/cm². In particular, a rangeof 2.12 to 4.25 W/cm² is preferable. Then, a predetermined electricvoltage is applied from the direct current power source 13 to theelectrode 6 a of the electrostatic chuck 6, so that the wafer W sticksto the electrostatic chuck 6 by means of Coulomb force, for example.

When the high-frequency electric power is applied to the supportingtable 2 as the lower electrode as described above, a high-frequencyelectric field is formed in the processing space between the showerhead16 as the upper electrode and the supporting table 2 as the lowerelectrode. Thus, the process gas supplied into the processing space ismade plasma, which etches the organic-material film 42. During theetching step, the resist film 45 functions as a mask partway. However,during the etching step, the resist film 45 and the BARC film 44 areetched to disappear. After that, only the inorganic-material film 43functions as a mask, and the etching process of the organic-materialfilm 42 is continued.

During the etching step, by means of the annular magnetic unit 21 of amulti-pole state, a magnetic field as shown in FIG. 2 can be formedaround the processing space. In the case, plasma confining effect isachieved, so that an etching rate of the wafer W may be made uniform,even in a case of a high frequency like this embodiment wherein theplasma tends to be not uniform. However, depending on the kind of thefilm, the magnetic field may not have an effect. In the case, thesegment magnets may be caused to revolve in order to conduct the etchingprocess under a condition wherein a magnetic field is substantially notformed around the processing space.

When the above magnetic field is formed, by means of the electricallyconductive or insulating focus ring 5 provided around the wafer W on thesupporting table 2, the effect of making the plasma process uniform canbe more enhanced. That is, if the focus ring 5 consists of anelectrically conductive material such as silicon or SiC, even afocus-ring region functions as the lower electrode. Thus, aplasma-forming region is expanded over the focus ring 5, the plasmaprocess around the wafer W is promoted, so that uniformity of theetching rate is improved. In addition, if the focus ring 5 consists ofan electrically insulating material such as quartz, electric charges cannot be transferred between the focus ring 5 and electrons and ions inthe plasma. Thus, the plasma confining effect may be increased so thatuniformity of the etching rate is improved.

In order to adjust plasma density and ion-drawing effect, thehigh-frequency electric power for generating plasma and a secondhigh-frequency electric power for drawing ions may be overlapped witheach other. Specifically, as shown in FIG. 10, in addition to thehigh-frequency electric power source 10 for generating plasma, a secondhigh-frequency electric power source 26 for drawing ions is connected tothe matching box 11, so that they are overlapped. In the case, thefrequency of the second high-frequency electric power source 26 fordrawing ions is preferably 3.2 to 13.56 MHz, in particular 13.56 MHz.Thus, the number of parameters for controlling ion energy is increasedso that an optimum processing condition can be easily set wherein anetching rate of the organic-material film is raised more while anecessary and sufficient etching selective ratio with respect to theinorganic-material film is assured.

Herein, according to a result of study by the inventors, in the etchingprocess of the organic-material film, the plasma density is dominant,and the ion energy contributes only a little. On the other hand, in theetching process of the inorganic-material film, both the plasma densityand the ion energy are necessary. Thus, when the organic-material film42 is etched by using the inorganic-material film 43 as a mask, in orderto etch the organic-material film 42 with a high etching rate and a highetching selective ratio with respect to the inorganic-material film 43,the plasma density has to be high and the ion energy has to be low. Thatis, if the ion energy necessary for etching the inorganic-material filmis low and the plasma density dominant for etching the organic-materialfilm is high, only the organic-material film can be selectively etchedwith a high etching rate. Herein, the ion energy of the plasmaindirectly corresponds to a self-bias electric voltage of an electrodeat the etching process. Thus, in order to etch the organic-material filmwith a high etching rate and a high etching selective ratio, finally, itis necessary to etch the organic-material film under a condition of highplasma density and low self-bias electric voltage.

This is explained with reference to FIG. 11 as follows. FIG. 11 is agraph showing relationships between a self-bias electric voltage Vdc andplasma density Ne, in respective cases wherein the frequency of thehigh-frequency electric power is 40 MHz or 100 MHz. The transverse axisrepresents the self-bias electric voltage Vdc, and the ordinate axisrepresents the plasma density. In the case, as the plasma gas, Ar wasused for evaluation, instead of real etching gas. For each frequency,applied high-frequency electric power was changed, so that values of theplasma density Ne and the self-bias electric voltage Vdc were changed.That is, in the respective frequencies, if the applied high-frequencyelectric power is large, both the plasma density Ne and the self-biaselectric voltage Vdc are large. Herein, the plasma density was measuredby means of a microwave interferometer.

As shown in FIG. 11, in the case wherein the frequency of thehigh-frequency electric power is conventionally 40 MHz, when the plasmadensity is increased to enhance the etching rate of the organic-materialfilm, the self-bias electric voltage Vdc is greatly increased. On theother hand, in the case wherein the frequency of the high-frequencyelectric power is 100 MHz that is higher than prior art, even when theplasma density is increased, the self-bias electric voltage Vdc is notso increased and controlled substantially not higher than 100 V. Thatis, it was found that a condition of high plasma density and lowself-bias electric voltage can be achieved. That is, if the frequency isrelatively low like a conventional art, when the etching rate of theorganic-material film is increased in a real etching process, theinorganic-material film is also etched to the same extent and goodselective-etching performance is not achieved. On the other hand, if thefrequency is as high as 100 MHz, it was found that the organic-materialfilm can be etched with a high etching rate and a high etching selectiveratio with respect to the inorganic-material film.

In addition, as seen from FIG. 11, in order to etch the organic-materialfilm with a high etching rate and a high etching selective ratio byhigher plasma density and lower self-bias electric voltage than priorart, when the plasma of Ar gas is formed, it may be thought preferableto form the plasma under a condition wherein the plasma density is notless than 1×10¹¹ cm⁻³ and the self-bias electric voltage of theelectrode is not higher than 300 V. More preferably, the plasma densityis not less than 1.5×10¹¹ cm⁻³ and the self-bias electric voltage of theelectrode is not higher than 100 V. Then, in order to satisfy such aplasma condition, it may be estimated that the frequency of thehigh-frequency electric power has to be 50 MHz or higher.

Thus, the frequency of the high-frequency electric power for generatingplasma is set not less than 50 MHz, as described above. However, if thefrequency of the high-frequency electric power for generating plasma ishigher than 150 MHz, the uniformity of the plasma may be deteriorated.Thus, it is preferable that the frequency of the high-frequency electricpower for generating plasma is not higher than 150 MHz. In particular,in order to effectively achieve the above effect, it is preferable thatthe frequency of the high-frequency electric power for generating plasmais 70 to 100 MHz.

Next, a measurement result of self-bias electric voltage and plasmadensity is explained wherein a real etching gas (N₂+H₂) is used and ahigh-frequency electric power of 100 MHz is applied. FIG. 12 is a graphcomparatively showing relationships between a self-bias electric voltageand plasma density, in respective cases wherein the plasma is formed byan Ar gas or an etching gas, when the frequency of the high-frequencyelectric power is 100 MHz. The transverse axis represents the self-biaselectric voltage Vdc, and the ordinate axis represents the plasmadensity. At that time, the pressure in the chamber was 13.3 Pa (100mTorr). Herein, the power of the high-frequency electric power of 100MHz was changed, so that the plasma density and the self-bias electricvoltage Vdc were changed. In addition, the power of the high-frequencyelectric power of 100 MHz was fixed to 2500 W while a secondhigh-frequency electric power of 3.2 MHz was overlapped in a range of200 to 3000 W.

As shown in FIG. 12, in the case of the plasma of real etching gas,compared with the plasma of Ar gas, the plasma density tends to be alittle lower. In addition, when the second high-frequency electric powerof the lower frequency (3.2 MHz) is overlapped and the power isincreased, the self-bias electric voltage tends to be increased.

As described above, in the case of the high frequency of 100 MHz, theplasma density tends to be higher and the self-bias electric voltagetends to be lower than the conventional art. Thus, in FIG. 12, in acondition wherein the plasma density of the etching gas at 1000 W is notless than 5×10¹⁰ cm⁻³, which corresponds to 1×10¹¹ cm⁻³ of the Arplasma, the etching process can be conducted with a high etching ratewhile satisfying an etching selective ratio with respect to theinorganic-material film.

When the second high-frequency electric power of 3.2 MHz is notoverlapped, at 2800 W, the plasma density becomes 1×10¹¹ cm⁻³ and theself-bias electric voltage becomes about 200 V. On the other hand, whenthe second high-frequency electric power of 3.2 MHz is overlapped andthe power is increased, at 3000 W, the plasma density becomes about1×10¹¹ to 2×10¹¹ cm⁻³ and the self-bias electric voltage becomes about800 to 900 V. When the overlapped power of 3.2 MHz is increased, it isthought that the etching rate is also increased. On the other hand, whenthe self-bias electric voltage is increased, the etching selective ratiowith respect to the inorganic-material film tends to be lowered.However, until the self-bias electric voltage reaches about 900 V, theetching selective ratio can be maintained in an allowable range. Thus,when the overlapped power (bias power) of the second high-frequencyelectric power is increased, the etching rate may be enhanced while anetching selective ratio of a desirable level is maintained. That is,under a condition wherein the plasma density is 5×10¹⁰ to 2×10¹¹ cm⁻³and the self-bias electric voltage of the electrode is not higher than900 V, it is possible that the etching process is conducted with a highetching rate while maintaining the etching selective ratio with respectto the inorganic-material film within a desirable range.

Next, specific preferable conditions are explained.

At first, they includes a condition wherein: a pressure in the chamber 1is 13.3 to 106.7 pa (100 to 800 mTorr) that is high; a firsthigh-frequency electric power having a frequency of 50 to 150 MHz, forexample 100 MHz, and a power density of 2.12 to 4.25 W/cm² is applied tothe supporting table 2; if necessary, a second high-frequency electricpower having a frequency of 500 kHz to 27 MHz, for example 3.2 MHz, anda power density of not higher than 4.25 W/cm² is applied to beoverlapped with the first high-frequency electric power; the plasmadensity is 5×10¹⁰ to 2×10¹¹ cm⁻³; and the self-bias electric voltage Vdcof the supporting table 2 as the lower electrode is not higher than 900V. Under the condition, since the pressure in the chamber 1 isrelatively high, vertical component of ion energy can be relativelyreduced. In addition, the bias power is adjusted so that theorganic-material film can be etched with a high etching selective ratiowith respect to the inorganic-material film and with a high etchingrate. In particular, when a hole is etched, a very high etching rate canbe achieved while a high etching selective ratio can be maintained.

In addition, they includes a condition wherein: a pressure in thechamber 1 is 1.33 to 6.67 pa (10 to 50 mTorr) that is low; a firsthigh-frequency electric power having a frequency of 50 to 150 MHz, forexample 100 MHz, and a power density of 2.12 to 4.25 W/cm² is applied tothe supporting table 2; if necessary, a second high-frequency electricpower having a frequency of 500 kHz to 27 MHz, for example 3.2 MHz, anda power density of not higher than 0.566 W/cm² is applied to beoverlapped with the first high-frequency electric power; the plasmadensity is 5×10¹⁰ to 2×10¹¹ cm⁻³; and the self-bias electric voltage Vdcof the supporting table 2 as the lower electrode is not higher than 400V. Under the condition, since the pressure in the chamber 1 is low, ionenergy itself can be controlled not higher than energy by which theinorganic-material film can be spattered. In addition, throughadjustment of the bias power or the like, the self-bias electric voltageis limited within the relatively low range. Thus, the organic-materialfilm can be etched with a high etching rate and a very high etchingselective ratio with respect to the inorganic-material film. Inaddition, surface residue is substantially not left. In addition, aCD-shift of the mask of the inorganic-material film can be remarkablyreduced.

Next, in order to obtain a real etching rate of an organic-material filmand an etching selective ratio with respect to an inorganic-materialfilm, etching experiments for whole-surface formed films of anorganic-material film (resist) and an inorganic-material film (SiO₂)were conducted. The result is explained. Herein, a 200 mm wafer is usedas the wafer W, an N₂ gas: 0.1 L/min and an O₂ gas: 0.01 L/min weresupplied as an etching gas, the gap between the electrodes was 27 mm,and the pressure in the chamber was 2.66 Pa.

FIG. 13A is a graph showing etching rates of an organic-material film ata wafer position, in respective cases wherein the high-frequencyelectric power is 500 W (1.59 W/cm²), 1000 W (3.18 W/cm²) or 1500 W(4.77 W/cm²), when the frequency of the high-frequency electric power is100 MHz. FIG. 13B is a graph showing etching rates of anorganic-material film at a wafer position, in respective cases whereinthe high-frequency electric power is 500 W (1.59 W/cm²), 1000 W (3.18W/cm²) or 1500 W (4.77 W/cm²), when the frequency of the high-frequencyelectric power is 40 MHz. FIG. 14 is a graph showing relationshipsbetween a high-frequency electric power and an etching rate of theorganic-material film, in respective cases wherein the frequency of thehigh-frequency electric power is 40 MHz or 100 MHz. FIG. 15 is a graphshowing relationships between a high-frequency electric power and anetching rate of the inorganic-material film, in respective cases whereinthe frequency of the high-frequency electric power is 40 MHz or 100 MHz.FIG. 16 is a graph showing relationships between an etching rate of theorganic-material film and a ratio (an etching rate of theorganic-material film/an etching rate of the inorganic-material film)corresponding to an etching selective ratio, in respective cases whereinthe frequency of the high-frequency electric power is 40 MHz or 100 MHz.

From these drawings, it can be seen that the etching rate of theorganic-material film is higher in the case of 100 MHz, for every power.When the high-frequency electric power is increased, the etching rate ofthe inorganic-material film tends to be increased. However, thedifference between the etching rate in the case of 40 MHz and theetching rate in the case of 100 MHz is not large. In addition, when thehigh-frequency electric power is higher, the etching rate of theorganic-material film is higher, and when the high-frequency electricpower is lower, the value corresponding to the etching selective ratiowith respect to the inorganic-material film tends to be higher. Inaddition, comparing the etching rate in the case of 40 MHz and theetching rate in the case of 100 MHz, when the value corresponding to theetching selective ratio is the same, the etching rate in the case of 100MHz is higher. Comparing them at the same etching rate, the valuecorresponding to the etching selective ratio in the case of 100 MHz islarger than the value corresponding to the etching selective ratio inthe case of 40 MHz. That is, from the experimental result of the samplesfor estimation, it was confirmed that the possibility of etching theorganic-material film with a high etching rate and a high etchingselective ratio is higher in the case of 100 MHz than in the case of 40MHz. The power of the high-frequency electric power of 100 MHz ispreferably in a range of about 1.0 W/cm² to about 5.0 W/cm², because theetching rate and the etching selective ratio of the organic-materialfilm are in a tradeoff relationship.

Next, regarding the wafer W having the structure (real pattern) shown inFIG. 9A, while the resist film 45 and the inorganic-material film 43consisting of SiO₂ were used as a mask, the organic-material film 42consisting of a low-k film was etched by the unit shown in FIG. 1 byusing the high-frequency electric power of 40 MHz and 100 MHz,respectively. The etching condition of this case was the same as that inthe above etching experiment of the whole-surface formed films. Herein,as the organic-material film 42, SiLK (commercial name) being a low-kfilm and made by DowChemical company was used. A thickness thereof was570 nm, a thickness of the SiO₂ film 43 thereon was 200 nm, a thicknessof the BARC film 44 thereon was 60 nm, and a thickness of the resistfilm 45 was 800 nm. The etching process was continued for a time that is1.5 times as long as that until the organic-material film 42 iscompletely etched (50% over etching). The time for which the SiO₂ filmis exposed to the plasma was lengthened. That is, the condition wassevere on the SiO₂ film.

The result is shown in FIGS. 17 and 18. FIG. 17 is a graph showingrelationships between a high-frequency electric power and an etchingrate of the organic-material film and relationships between ahigh-frequency electric power and a shoulder loss of theinorganic-material film. FIG. 18 is a graph showing relationshipsbetween an etching rate of the organic-material film and an etchingselective ratio with respect to an etching rate of a shoulder part ofthe inorganic-material film, in respective cases wherein the frequencyof the high-frequency electric power is 40 MHz or 100 MHz. Herein, theshoulder loss means an etched volume of the shoulder part. Specifically,as shown in FIG. 19, the shoulder loss means a height distance (shown byY in the drawing) from the original surface of the inorganic-materialfilm 43 to an etched (deepest) position of the shoulder part. Inaddition, the etching selective ratio at the shoulder part in FIG. 18means a ratio of the etching rate of the organic-material film withrespect to the etching rate at the shoulder part of theinorganic-material film 43 calculated from the value of the shoulderloss.

As shown in FIG. 17, in the respective high-frequency electric powers,when the respective results in the cases of 100 MHz and 40 MHz arecompared with each other, the shoulder loss is at the same level, butthe etching rate of the organic-material film is higher in the case of100 MHz. In addition, as shown in FIG. 18, in the real pattern, in thesame manner as FIG. 16 showing the results of the samples forestimation, when the etching selective ratio is the same, the etchingrate of the organic-material film is higher in the case of 100 MHz. Whenthe etching rate is the same, the etching selective ratio tends to behigher in the case of 100 MHz. That is, in the etching process of thereal pattern, it was confirmed that the organic-material film can beetched with a high etching rate and a high etching selective ratio whenthe high-frequency electric power of 100 MHz, other than 40 MHz, isused.

In the above experiment, the gap between the electrodes was 27 mm. Asdescribed above, if the distance between the electrodes is too small,pressure distribution (pressure difference between at a central portionand at a peripheral portion) on the surface of the wafer W, which is asubstrate to be processed, becomes so large that deterioration of theetching uniformity or the like may be generated. Thus, in practice, thedistance between the electrodes is preferably 35 to 50 mm. This isexplained with reference to FIG. 20.

FIG. 20 is a graph comparatively showing relationships between an Ar-gasflow rate and a pressure difference ΔP of a central portion of the waferand a peripheral portion thereof, in respective cases wherein theelectrode gap is 25 mm or 40 mm, wherein the Ar gas is used as a plasmagas. As shown in FIG. 20, the pressure difference ΔP is smaller when thegap is 40 mm rather than 25 mm. In addition, in the case of the gap of25 mm, when the Ar-gas flow rate is increased, the pressure differenceΔP tends to be sharply increased. When the gas flow rate is higher thanabout 0.3 L/min, it exceeds 0.27 Pa (2 mTorr) as an allowable maximumpressure difference ΔP, at which deterioration of the etching uniformityor the like may not be generated. On the other hand, in the case of thegap of 40 mm, independently on the gas flow rate, the pressuredifference is smaller than 0.27 Pa (2 mTorr). Thus, it can be expectedthat the allowable maximum pressure difference ΔP at which deteriorationof the etching uniformity or the like may not be generated is ensured,independently on the gas flow rate, if the electrode gap is not lessthan about 35 mm.

Next, regarding a 300 mm wafer having the real pattern shown in FIG. 9A,respective films having the same thicknesses as the example shown inFIGS. 17 and 18, while the resist film 45 and the inorganic-materialfilm 43 consisting of SiO₂ were used as a mask, the organic-materialfilm 42 consisting of a low-k film was etched. Herein, according to themanner shown in FIG. 10, two high-frequency electric power sources of100 MHz and 3.2 MHz were connected to the supporting table 2, thehigh-frequency electric power of 100 MHz was fixed to 2400 W, and thesecond high-frequency electric power of 3.2 MHz was changed between 0 W,200 W, 800 W, 1600 W and 3000 W. As the process gas, an N₂ gas and an H₂gas were used. The pressure in the chamber was changed between 13.3 Pa(100 mTorr), 31.7 Pa (450 mTorr) and 106.7 Pa (800 mTorr). The flow rateof the process gas was the N₂ gas: 0.5 L/min and the H₂ gas: 0.5 L/minin the case of 13.3 Pa, and the N₂ gas: 0.65 L/min and the H₂ gas: 0.65L/min in the cases of 31.7 Pa and 106.7 Pa. The electrode gap was 40 mm.The etching process was conducted as 50% over etching in the same manneras the above example.

The result is shown in FIGS. 21 to 23. FIG. 21 is a graph showingrelationships between the power of the second high-frequency electricpower of 3.2 MHz and an etching rate of the organic-material film andrelationships between the power of the second high-frequency electricpower of 3.2 MHz and an etching selective ratio with respect to theshoulder part, in respective pressure conditions. FIG. 22 is a graphshowing relationships between the power of the second high-frequencyelectric power of 3.2 MHz and a top CD shift, in respective pressureconditions. FIG. 23 is a graph showing relationships between the powerof the second high-frequency electric power of 3.2 MHz and a bowingvalue, in respective pressure conditions. Herein, as shown in FIG. 24,the top CD shift means a value showing how much a top CD is changedthrough the etching process, the top CD meaning an etching opening at anupper-end portion of the organic-material film 42. That is, the top CDshift means a value obtained by subtracting an original top CD (TopCDbf)from a top CD after the etching process (TopCDaf). In addition, thebowing value means a value obtained by subtracting the top CD (TopCD)from a maximum width (MaxCD) at an etched portion after the etchingprocess of the organic-material film.

In the example, since the pressure in the chamber is 13.3 Pa or higher,ion dispersion is great, so that vertical component of ion energy isrelatively reduced. Thus, as shown in FIG. 21, when the power of thesecond high-frequency electric power (bias power) of 3.2 MHz isrelatively low, the inorganic-material mask is hardly etched. That is,the organic-material film can be etched with a high etching selectiveratio with respect to the inorganic-material mask. Furthermore, in thecase, the etching rate of the organic-material film is also high. Inaddition, at the same bias power, the etching selective ratio tends tobe higher under a condition of a higher pressure wherein the verticalcomponent of ion energy is less. In addition, in each pressure, when thepower of the second high-frequency electric power of 3.2 MHz isincreased, the etching rate of the organic-material film is increasedwhile the etching selective ratio at the shoulder portion tends to belowered. If the power of the second high-frequency electric power of 3.2MHz is low, an ion-drawing force to the wafer is weak so that ions aresupplied to the inorganic-material mask only very softly. Thus, theinorganic-material mask is hardly etched, so that a high etchingselective ratio can be obtained. On the other hand, when the power ofthe second high-frequency electric power of 3.2 MHz is increased, theion-drawing force to the wafer becomes stronger, so that the etchingrate of the organic-material film is increased but the etching rate ofthe inorganic-material film is also increased. Thus, the etchingselective ratio is deteriorated. In the case of the pressure of 13.3 Pa,when the bias power is 1600 W (power density: 2.26 W/cm²) that is high,the etching rate of the organic-material film is 400 nm/min that ishigh, but the etching selective ratio is reduced to about 3 or 4. Thisfeature is usable for some applications. However, it can be expectedthat a bias power higher than the above is not usable because theetching loss of the inorganic-material mask is too much. In the case ofthe pressure of 106.7 Pa, even when the bias power is 3000 W (powerdensity: 4.25 W/cm²), the etching selective ratio is maintained at about5. This feature is usable for some applications. Then, the etching rateof the organic-material film is 550 nm/min, which is very high. However,even in the case of the pressure of 106.7 Pa, it is expected that a biaspower higher than 3000 W (power density: 4.25 W/cm²) is not usablebecause the etching loss of the inorganic-material mask is too much.

As shown in FIG. 22, the top CD shift tends to be better in the case ofthe pressure of 13.3 Pa than in the case of the pressure of 106.7 Pa.Furthermore, in the case of 13.3 Pa, when the bias power is increased,the top CD shift is reduced, and when the bias power is 1600 W (powerdensity: 2.26 W/cm²), the top CD shift is about 2 to 3 nm. In the caseof the pressure of 106.7 Pa, independently on the bias power, the top CDshift is 30 nm. In the case of the pressure of 106.7 Pa, the top CDshift is near to the upper limit of an allowable range. Thus, thesubstantially upper limit of the pressure in the chamber is 106.7 Pa.

As shown in FIG. 23, the bowing value tends to be lower in the case ofthe pressure of 106.7 Pa than in the case of the pressure of 13.3 Pa, atthe same bias power. In addition, in the case of 106.7 Pa, when the biaspower is increased, the bowing value is increased, and when the biaspower is 3000 W (power density: 4.25 W/cm²), the bowing value is 30 nm.When the bias power is higher than 3000 W, it is expected that thebowing value exceeds 30 nm. Thus, the upper limit of the bias power is3000 W (power density: 4.25 W/cm²).

Next, regarding a 300 mm wafer having the real pattern shown in FIG. 9A,respective films having the same thicknesses as the example shown inFIGS. 17 and 18, while the resist film 45 and the inorganic-materialfilm 43 consisting of SiO₂ were used as a mask, the organic-materialfilm 42 consisting of a low-k film was etched. Herein, according to themanner shown in FIG. 10, two high-frequency electric power sources of100 MHz and 3.2 MHz were connected to the supporting table 2, thehigh-frequency electric power of 100 MHz was fixed to 2400 W, and thesecond high-frequency electric power of 3.2 MHz was changed between 0 W,200 W and 400 W. As the process gas, an N₂ gas and an H₂ gas were used.The pressure in the chamber was changed between 1.33 Pa (10 mTorr), 3.99Pa (30 mTorr), 6.65 Pa (50 mTorr) and 13.3 Pa (100 mTorr). The flow rateof the process gas was the N₂ gas: 0.12 L/min and the H₂ gas: 0.12 L/minin the case of 1.33 Pa, the N₂ gas: 0.18 L/min and the H₂ gas: 0.18L/min in the cases of 3.99 Pa, the N₂ gas: 0.3 L/min and the H₂ gas: 0.3L/min in the cases of 6.65 Pa and the N₂ gas: 0.5 L/min and the H₂ gas:0.5 L/min in the cases of 13.3 Pa. The electrode gap was 40 mm. Theetching process was conducted as 50% over etching in the same manner asthe above examples.

For each sample after the etching process, an etching residue, ashoulder loss of the inorganic-material film (mask) and a top CD shiftwere obtained. The result is shown in FIGS. 26 and 27. FIG. 26 is agraph showing etching residues, shoulder losses of theinorganic-material film (mask) and top CD shifts, in respective pressureconditions, when the bias power (of the second high-frequency electricpower source) is zero. FIG. 27 is a graph showing shoulder losses of theinorganic-material film (mask), top CD shifts and etching rates of theorganic-material film, in respective bias-power conditions, when thepressure is 3.99 Pa.

As shown in FIG. 26, no etching reside was generated when the pressurewas 6.65 Pa or lower, but some etching reside was generated when thepressure was 13.3 Pa. The shoulder loss of the inorganic-material filmwas 0 in the cases of 3.99 Pa, 6.65 Pa and 13.3 Pa. The shoulder loss ofthe inorganic-material film was 42 nm in the case of 1.33 Pa, whichvalue is relatively large but within an allowable range. The top CDshift was −3 nm in the case of 3.99 Pa, and +5 nm in the case of 6.65Pa, which values are very small. In addition, it was confirmed that theabsolute value of the top CD shift is increased both when the pressureis higher than 6.65 Pa and when the pressure is lower than 3.99 Pa. Thetop CD shift was −30 nm in the case of 1.33 Pa, which value isapproximately within an allowable range. From these results, it wasconfirmed that the pressure is preferably within a range of 1.33 to 6.65Pa in order to conduct an etching process wherein the shoulder loss issmall (that is, the etching selective ratio is high), the etchingresidue is less, and the top CD shift is small.

In addition, as shown in FIG. 27, when the bias power is increased, theshoulder loss tends to be increased and the absolute value of the top CDshift tends to be increased. However, when the bias power is 400 W(power density: 0.566 W/cm²) or lower, the respective values of theshoulder loss and the top CD shift were within usable ranges. It isestimated that the shoulder loss becomes too large when the bias powerexceeds 400 W. In addition, the etching rate tends to be increased whenthe bias power is increased.

From the above results, it was confirmed that: in order to enhance theetching selective ratio, to reduce the top CD shift, and to preventgeneration of the etching residue, it is sufficient that the pressure inthe chamber is 1.33 Pa to 6.65 Pa and the bias power density is nothigher than 0.566 W/cm².

The present invention is not limited to the above embodiment, but may bevariously modified. For example, in the above embodiment, as themagnetic-field generating means, the annular magnetic unit in themulti-pole state is used wherein the plurality of segment magnetsconsisting of permanent magnets are arranged annularly around thechamber. However, the present invention is not limited to this manner ifa magnetic-field can be formed around the processing space to confinethe plasma. In addition, the peripheral magnetic field for confining theplasma may be unnecessary. That is, the etching process can be conductedunder a condition wherein there is no magnetic field. In addition, thepresent invention can be applied to a plasma etching process conductedin a crossed electromagnetic field wherein a horizontal magnetic fieldis applied to the processing space. In addition, in the aboveembodiment, the high-frequency electric power for generating plasma isapplied to the lower electrode, but may be applied to the upperelectrode. In the above embodiment, the low-k film is used as theorganic-material film, but other films including O, C and H or otherfilms including Si, O, C and H may be also used. In addition, thesemiconductor wafer is taken as an example of the substrate to beprocessed. However, this invention is not limited thereto, butapplicable to other plasma processes for an LCD substrate or the like.In addition, the above description is about the case wherein theorganic-material film is etched by using the inorganic-material film asa mask, but this invention is not limited thereto. This invention isapplicable to all cases to selectively etch an organic-material filmwith respect to an inorganic-material film. For example, this inventionis applicable to an ashing process to remove a resist that has been usedas a mask when an inorganic-material film, for example a SiO₂ film,formed on a substrate to be processed, for example a Si wafer or thelike, is etched. The ashing process has to be conducted so as toselectively and efficiently remove the resist film being anorganic-material film, with etching the inorganic-material film underthe resist film as little as possible. Thus, if the present invention isapplied to the ashing process, a good ashing characteristic can beachieved.

1-26. (canceled)
 27. A plasma etching unit for selectivelyplasma-etching an organic-material film of a substrate having theorganic-material film and an inorganic-material thereon while using theinorganic-material film to function as a mask, said unit comprising: achamber configured to contain the substrate to be processed, first andsecond electrodes oppositely arranged in the chamber, the secondelectrode being configured to support the substrate to be processed, aprocess-gas supplying system configured to supply a process gas into thechamber, a gas-discharging system configured to discharge a gas in thechamber, and a first high-frequency electric power source configured tosupply a high-frequency electric power of 50 MHz to 150 MHz for forminga plasma to the second electrode, a second high-frequency electric powersource configured to apply a second high-frequency electric power of 500kHz to 27 MHz to the second electrode, the second high-frequencyelectric power being overlapped with the first high-frequency electricpower, and a magnetic-field forming unit configured to form a magneticfield around a plasma region between the first and second electrodes,wherein the magnetic-field forming unit consists of a magnetic annularunit having a plurality of rotatable, segment magnets concentricallyarranged around the chamber in such a manner that magnetic-poledirections of adjacent two segment magnets are opposite, and that avertical gap is set between pair of magnets.
 28. A plasma etching unitaccording to claim 27, wherein the second high-frequency electric poweris 13.56 MHz.
 29. A plasma etching unit according to claim 27, whereinthe second high-frequency electric power is 3.2 MHz.
 30. A plasmaetching unit according to claim 27, wherein a distance between the firstand second electrodes is shorter than 50 mm.
 31. A plasma etching unitaccording to claim 27, wherein a strength of the magnetic field formedaround the plasma region between the first and second electrodes by themagnetic-field forming unit is 0.03 to 0.045 T (300 to 450 Gauss).
 32. Aplasma etching unit according to claim 27, wherein a focus ring isprovided around the substrate to be processed, and when themagnetic-field forming unit forms a magnetic field around the plasmaregion between the first and second electrodes, a strength of themagnetic field on the focus ring is not lower than 0.001 T (10 Gauss)and a strength of the magnetic field on the substrate to be processed isnot higher than 0.001 T.
 33. A plasma etching unit according to claim27, wherein power density of the first high-frequency electric power is2.12 to 4.25 W/cm².
 34. A plasma etching unit according to claim 27,wherein the gas-discharging system is configured to make a pressure inthe chamber be 13.3 to 106.7 Pa.
 35. A plasma etching unit according toclaim 27, wherein the gas-discharging system is configured to make apressure in the chamber be 1.33 to 6.67 Pa.
 36. A plasma etching unitaccording to claim 27, wherein a power density of the secondhigh-frequency electric power is not higher than 4.25 W/cm².